Mo O'Neil Osorio wrote: "The situation is under control. No reports that the shooter has fired his/her weapon at anyone, just up in the air as the initial shots to alarm people.

"A friend of mine is in school at the building next door. Military personnel are handling this with heavy ground and sdpd/swat/k9 is assisting."

The centre had more than 1.2 million outpatient visits in 2014, admitting more than 19,000 patients.

(Photo: Google Street View)

Garfield High School (Photo: Google Street View)

Lockdown: There schools are reportedly on lock down in the area - San Diego High School, Roosevelt Middle School and Garfield Middle School (Photo: Google Street View)

A statement was issued by the naval centre.

It says: "According to initial reports of a single witness, at approximately 8a this morning three shots were reportedly heard in the basement of Building 26, a combination gym / barracks, at the Navy Medical Center Balboa Park facility. "